Vitamin D and its metabolites are necessary for the maintenance of calcium homeoslasis. More than 20 metabolites have been discovered to date, varying greatly in biological activity. See, for example, U.S. Pat. No. 3,697,559 which discloses 1,25-dihydroxycholecalciferol which has vitamin D like activity in promoting intestinal calcium absorption.
The novel compounds of this invention are biologically active in terms of both bone calcium mobilization and intestinal calcium absorption and they have been shown to bind to the chick intestinal 1,25(OH).sub.2 D.sub.3 receptor protein; this receptor protein is believed to mediate the biological responses to these compounds. They are therefore both of clinical importance in treatment of disease states involving calcium homeostasis disorders such as renal osteodystrophy, osteoporosis, hypoparathyroidism, and stereoid-induced osteopenia.
The two new vitamin D metabolites of this invention were isolated in pure form from separate incubations of homogenates of chick small intestinal mucosa or rat kidney employing either 1.alpha.,25-dihydroxyvitamin D.sub.3 [28 .mu.M] or 1.alpha.,24R,25-trihydroxy-vitamin D.sub.3 as substrate [0.17-1.3 .mu.M]. The newly characterized compounds and the amounts isolated in pure form from separate isolations are respectively: 1.alpha.,25-dihydroxy-24-oxo-vitamin D.sub.3 [1,25(OH).sub.2 -24-oxo-D.sub.3 ], 147 .mu.g (from kidney), 4.2 and 40 .mu.g (from intestine) and 1.alpha.,23,25-trihydroxy-24-oxo-vitamin D.sub.3 [1,23,25(OH).sub.3 -24-oxo-D.sub.3 ] 155 .mu.g (from kidney), 5.9 and 34 .mu.g (from intestine). Their structures were identified after extensive analysis, as well as direct comparison with synthetic 1,25(OH).sub.2 -24-oxo-D.sub.3. The isolation in pure form and these structural assignments for both compounds correct previous determinations which had been proposed based on impure materials [N. Ohnuma et al. (1982) J. Biol. Chem. 257, 5097-5102].